Thermal processes and secondary recycling regulate the atmospheric levels of the highly toxic polychlorinated naphthalenes in an urban Mediterranean site.

Although production of legacy industrial-grade Persistent Organic Pollutants (POPs) has been prohibited since the early 00’s, residues are still present in all environmental compartments, whereas illicit usage is still documented at a global scale. Unauthorized disposal activities of Aroclor technical mixtures and illegal incineration of obsolete electronic equipment are also primary sources of significant environmental concern.

Island of Cyprus, situated at the easternmost side of the Mediterranean Basin, is surrounded by large urban and industrial areas and comprises a unique location for exploring air quality over the broader Eastern Mediterranean and Middle East (EMME) region. The present work extends previous reports on the occurrence and fate of a wide spectrum of highly toxic compounds in the atmosphere over Cyprus and explores comprehensively the atmospheric distribution of polychlorinated naphthalenes (PCNs) and polybrominated diphenyl ethers (PBDEs), both listed under the Stockholm Convention text.

Total (gaseous and particulate phase) concentrations of the scarcely monitored in EMME region PCNs were measured similar to urban locations. Contrarily, the corresponding levels of PBDEs were comparable to background areas, exhibiting a relative enrichment in congeners with intermediate degree of bromination. Regressions of logarithms of partial pressure against ambient temperature for PCNs revealed that secondary recycling from contaminated terrestrial surfaces regulates their atmospheric variability. Enthalpies of surface-air exchange (ΔH_sa) for PCNs were significantly correlated to vaporization enthalpies (ΔH_v) determined by chromatography, corroborating the presence of short-range revolatilization processes. Homologue concentration ratios of PCNs suggested inputs from thermal processes, whereas potential evaporation from Aroclor-contaminated surfaces cannot be excluded. An inverse pattern for PBDEs was observed. The corresponding regression slopes were shallow, implying long-range atmospheric transport, whereas ΔH_sa were insignificantly correlated with ΔH_v, suggesting that, unlike PCNs, volatilization sources of PBDEs are of minor importance.

We also evaluated gas/particle partitioning by utilizing a comprehensive range of traditional and novel partitioning models. Additionally, we constructed, separately for PCNs and PBDEs, temperature-dependent quantitative structure-property relationship (QSPR) models based on quantum-mechanical descriptors. Equilibrium-state models predicted well the gas/particle partitioning quotients (K_p) of PCNs, whereas steady-state models predicted better the partitioning behavior of PBDEs. Both empirical QSPR models exhibited equal performance in predicting K_p and can be used as reference for studies under similar temperature ranges around the globe.

Acknowledgements: The present work received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No. 856612 (EMME-CARE) and the Cyprus Government.